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Plague Vaccine

MMWR 31(22);301-304

Publication date: 06/11/1982

Table of Contents

Article

SUMMARY

These revised ACIP recommendations on plague vaccine represent an
update of the previous recommendations (MMWR 1978;27:255-8) to include
current information and practices.

INTRODUCTION

Plague is a natural infection of rodents and their ectoparasites
and occurs in many parts of the world, including the western United
States. In this country, a few human cases develop each year
following exposure to infected wild rodents or their fleas and, less
commonly, to other infected wild animals (bobcats, coyotes, rabbits)
and domestic animals (cats, dogs). Epidemic plague may result when
domestic rat populations and their fleas become infected. Recently,
the areas of the most intensive epidemic and epizootic infection have
been some countries in Africa, Asia, and South America.

General Recommendations

Because human plague is rare in most parts of the world, there is
no need to vaccinate persons other than those at particularly high
risk of exposure. Routine vaccination is not necessary for persons
living in areas with enzootic plague such as the western United
States. It is not indicated for most travelers to countries reporting
cases, * particularly if their travel is limited to urban areas with
modern hotel accommodations.

Many plague patients in the western United States are infected as
a direct result of wild-rodent plague in the immediate vicinity of
their homes. Recommended risk-reduction measures include eliminating
wild-rodent harborage and food sources near homes, ridding pet dogs
and cats of fleas at least weekly, and avoiding direct contact with
sick or dead rodents.

In most countries of Africa, Asia, and South America where plague
is reported, the risk of exposure exists primarily in rural
mountainous or upland areas. Following natural disasters and at times
when regular sanitary practices are interrupted, plague can extend
from its usual areas of endemicity into urban centers. Rarely,
pneumonic plague has been reported in conjunction with outbreaks of
bubonic plague, and tourist travel to areas with reported cases of
plague should be avoided.

Routine bacteriologic precautions, including the use of a
biological safety cabinet to isolate procedures that may produce
aerosols, are sufficient to prevent accidental infection with plague
among clinical laboratory workers. Few laboratory-associated cases
have ever been reported, and these almost exclusively occurred at
plague research laboratories or involved unusual exposures.
Vaccination of clinical laboratory workers is not indicated.

Ecologists and other field workers who might come in contact with
wild animals and their ectoparasites in areas where plague has been
known to occur should be made aware of the potential risks of plague
and told how to minimize direct contact with potentially infective
animals and their tissues or parasites. These precautionary measures
are generally sufficient to prevent infection.

PLAGUE VACCINE

Plague vaccines ** have been used since the late 19th century, but
their effectiveness has never been measured precisely. Field
experience indicates that vaccination with plague vaccine reduces the
incidence and severity of disease resulting from the bite of infected
fleas. The degree of protection afforded against primary pneumonic
infection is not known. Persons exposed to plague patients who have
pneumonia or to Yersinia pestis *** aerosols in the laboratory should
be given a 7- to 10-day course of antimicrobic therapy regardless of
vaccination history. Recommended antimicrobials include tetracyclines,
chloramphenicol, or streptomycin.

The plague vaccine licensed for use in the United States is
prepared from Y. pestis organisms grown in artificial media,
inactivated with formaldehyde, and preserved in 0.5% phenol. The
vaccine contains trace amounts of beef-heart extract, yeast extract,
agar, and peptones and peptides of soya and casein.

Serum antibody to Fraction I capsular antigen, as measured by the
passive hemagglutination (PHA) test, is correlated with resistance to
Y. pestis infection in experimental animals. A comparable correlation
between PHA titer and immunity probably occurs in humans.

Following the primary series of 3 injections, about 7% of
individuals do not produce PHA antibody, and a few fail to develop a
titer of 128, the level correlated with immunity in experimental
animals. PHA titers should be determined for individuals who have an
unusually high risk of infection or who have a history of serious
reactions to the vaccine in order to govern the frequency of booster
doses. Such testing can be arranged through state health
departments. Since plague vaccination may only ameliorate illness,
whenever a vaccinated person has a definite exposure, prophylactic
antibiotics may be indicated whether or not an antibody response has
been demonstrated.

Vaccine Recipients

Vaccination is recommended for:

1) All laboratory and field personnel who are working with Y. pestis
organisms resistant to antimicrobics, 2) Persons engaged in aerosol
experiments with Y. pestis and 3) Persons engaged in field operations in
areas with enzootic plague where preventing exposure is not possible (such
as some disaster areas).

Selective plague vaccination should be considered for:

1) Laboratory personnel regularly working with Y. pestis or
plague-infected rodents, 2) Workers (for example, Peace Corps volunteers
and agricultural advisors) who reside in rural areas with enzootic or
epidemic plague where avoidance of rodents and fleas is impossible, and 3)
Persons whose vocation brings them into regular contact with wild rodents
or rabbits in areas with enzootic plague.

Primary Vaccination

All injections should be given intramuscularly.

Adults and children greater than or equal to 11 years old: The
primary series consists of 3 doses of vaccine. The first dose, 1.0
ml, is followed by the second dose, 0.2 ml, 4 weeks later. The third
dose, 0.2 ml, is administered 6 months after the first dose. If an
accelerated schedule is essential, 3 doses of 0.5 ml each,
administered at least 1 week apart, may be given. The efficacy of
this schedule has not been determined.

Children less than or equal to 10 years old: The primary
series is also 3 doses of vaccine, but the doses are smaller
(Table 1). The intervals between injections are the same as for
adults.

Booster Doses

When needed because of continuing exposure, 3 booster doses should
be given at approximately 6-month intervals. Thereafter, antibody
levels decline slowly and booster doses at 1- to 2-year intervals,
depending on the degree of continuing exposure, should provide good
protection.

The recommended booster dosages for children and adults are the
same as the second and third doses in the primary series. However, if
serious side effects to the vaccine occur, their severity may be
reduced by using half the usual dose. The primary series need never
be repeated for booster doses to be effective (Table 1).

SIDE EFFECTS OF VACCINE

Primary vaccination may result in general malaise, headache,
fever, mild lymphadenopathy, and erythema and induration at the
injection site in about 10% of recipients. These reactions occur more
commonly with repeated injections. Sterile abscesses occur rarely.
Rare cases of sensitivity reactions manifested by urticarial and
asthmatic phenomena have been reported.

PRECAUTIONS AND CONTRAINDICATIONS

Plague vaccine should not be administered to anyone with a known
hypersensitivity to any of the constituents, such as beef protein,
soya, casein, and phenol. Patients who have had severe local or
systemic reactions to plague vaccine should not be revaccinated.

The safety or efficacy of vaccination with plague vaccine during
pregnancy has not been determined, and therefore it should not be used
unless there is a substantial risk of infection.

* For a current listing, consult the most recent issue of the World
Health Organization's Weekly Epidemiological Record; current
information is also available from the Quarantine Division, Center for
Prevention Services, Centers for Disease Control, Atlanta, Georgia
30333.
** Official name: Plague Vaccine

*** The designation Yersinia pestis is used advisedly since there is
reportedly a recommendation by the International Committee on
Systematic Bacteriology to reclassify this organism as Yersinia
pseudotuberculosis ssp. pestis (WHO. Weekly Epidemiological Record
1981;56:399).

Meyer KF. Effectiveness of live or killed plague vaccines in man.
Bull WHO 1970;42:653-66.

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